/*****************************************************************************
** $Source: /cygdrive/d/Private/_SVNROOT/bluemsx/blueMSX/Src/IoDevice/WDCRC.c,v $
**
** $Revision: 1.4 $
**
** $Date: 2008-03-30 18:38:41 $
**
** Description: Calculates a 16-bit Cyclic Redundancy Check (CRC) that is
**              compliant with the CCITT/ITU standard.
**              Synthetic polynomial = x^16 + x^12 + x^5 + 1
**              Truncated polynomial = 0x1021
**              Initial value = 0xFFFF
**
** More info: http://www.bluemsx.com
**
** Copyright (C) 2003-2006 Daniel Vik, Tomas Karlsson
**
** This program is free software; you can redistribute it and/or modify
** it under the terms of the GNU General Public License as published by
** the Free Software Foundation; either version 2 of the License, or
** (at your option) any later version.
** 
** This program is distributed in the hope that it will be useful,
** but WITHOUT ANY WARRANTY; without even the implied warranty of
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
** GNU General Public License for more details.
**
** You should have received a copy of the GNU General Public License
** along with this program; if not, write to the Free Software
** Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
**
******************************************************************************
*/
#include "WDCRC.h"

/* CRC-CCITT Lookup Table */
unsigned short const wdcrcTable[256] = {
	0x0000,0x1021,0x2042,0x3063,0x4084,0x50A5,0x60C6,0x70E7,
	0x8108,0x9129,0xA14A,0xB16B,0xC18C,0xD1AD,0xE1CE,0xF1EF,
	0x1231,0x0210,0x3273,0x2252,0x52B5,0x4294,0x72F7,0x62D6,
	0x9339,0x8318,0xB37B,0xA35A,0xD3BD,0xC39C,0xF3FF,0xE3DE,
	0x2462,0x3443,0x0420,0x1401,0x64E6,0x74C7,0x44A4,0x5485,
	0xA56A,0xB54B,0x8528,0x9509,0xE5EE,0xF5CF,0xC5AC,0xD58D,
	0x3653,0x2672,0x1611,0x0630,0x76D7,0x66F6,0x5695,0x46B4,
	0xB75B,0xA77A,0x9719,0x8738,0xF7DF,0xE7FE,0xD79D,0xC7BC,
	0x48C4,0x58E5,0x6886,0x78A7,0x0840,0x1861,0x2802,0x3823,
	0xC9CC,0xD9ED,0xE98E,0xF9AF,0x8948,0x9969,0xA90A,0xB92B,
	0x5AF5,0x4AD4,0x7AB7,0x6A96,0x1A71,0x0A50,0x3A33,0x2A12,
	0xDBFD,0xCBDC,0xFBBF,0xEB9E,0x9B79,0x8B58,0xBB3B,0xAB1A,
	0x6CA6,0x7C87,0x4CE4,0x5CC5,0x2C22,0x3C03,0x0C60,0x1C41,
	0xEDAE,0xFD8F,0xCDEC,0xDDCD,0xAD2A,0xBD0B,0x8D68,0x9D49,
	0x7E97,0x6EB6,0x5ED5,0x4EF4,0x3E13,0x2E32,0x1E51,0x0E70,
	0xFF9F,0xEFBE,0xDFDD,0xCFFC,0xBF1B,0xAF3A,0x9F59,0x8F78,
	0x9188,0x81A9,0xB1CA,0xA1EB,0xD10C,0xC12D,0xF14E,0xE16F,
	0x1080,0x00A1,0x30C2,0x20E3,0x5004,0x4025,0x7046,0x6067,
	0x83B9,0x9398,0xA3FB,0xB3DA,0xC33D,0xD31C,0xE37F,0xF35E,
	0x02B1,0x1290,0x22F3,0x32D2,0x4235,0x5214,0x6277,0x7256,
	0xB5EA,0xA5CB,0x95A8,0x8589,0xF56E,0xE54F,0xD52C,0xC50D,
	0x34E2,0x24C3,0x14A0,0x0481,0x7466,0x6447,0x5424,0x4405,
	0xA7DB,0xB7FA,0x8799,0x97B8,0xE75F,0xF77E,0xC71D,0xD73C,
	0x26D3,0x36F2,0x0691,0x16B0,0x6657,0x7676,0x4615,0x5634,
	0xD94C,0xC96D,0xF90E,0xE92F,0x99C8,0x89E9,0xB98A,0xA9AB,
	0x5844,0x4865,0x7806,0x6827,0x18C0,0x08E1,0x3882,0x28A3,
	0xCB7D,0xDB5C,0xEB3F,0xFB1E,0x8BF9,0x9BD8,0xABBB,0xBB9A,
	0x4A75,0x5A54,0x6A37,0x7A16,0x0AF1,0x1AD0,0x2AB3,0x3A92,
	0xFD2E,0xED0F,0xDD6C,0xCD4D,0xBDAA,0xAD8B,0x9DE8,0x8DC9,
	0x7C26,0x6C07,0x5C64,0x4C45,0x3CA2,0x2C83,0x1CE0,0x0CC1,
	0xEF1F,0xFF3E,0xCF5D,0xDF7C,0xAF9B,0xBFBA,0x8FD9,0x9FF8,
	0x6E17,0x7E36,0x4E55,0x5E74,0x2E93,0x3EB2,0x0ED1,0x1EF0
};

UInt16 calc_crc(UInt16 crc, UInt8 value)
{
	return (((crc)<<8)^wdcrcTable[((crc)>>8)^(value)]);
}
